Aircraft engine nacelle inlet having access opening for electrical ice protection system

ABSTRACT

An aircraft engine nacelle inlet is provided with an inlet cowling. The inlet cowling includes an inner lip, an outer lip, and a leading edge portion connecting the inner and outer lips. Heating elements are provided proximate the leading edge, either on an inside surface of the cowling or on an outside surface. An inner barrel portion and an outer barrel portion of the nacelle inlet define a space therebetween. Ice protection-related equipment such as controllers, cables, switches, connectors, and the like, may reside in this space. One or more access openings are formed in the outer barrel to enable an operator to gain access to this equipment. The inlet cowling attaches to the inner and outer barrels with its outer lip extending sufficiently far in the aft direction to cover the access opening. When the cowling is removed, the access opening is uncovered, thereby permitting access to the equipment.

RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. ______,“Aircraft Engine Nacelle Inlet Having Electrical Ice Protection System”,filed even date herewith by the same inventors as the presentapplication, and having substantially the same specification.

BACKGROUND

The invention relates to ice protection systems for aircraft, and morespecifically relates to an aircraft equipped with a low power highefficiency electrical ice protection system.

The accumulation of ice on aircraft wings and other structural membersin flight is a danger that is well known. Such “structural members”include any aircraft surface susceptible to icing during flight,including wings, stabilizers, rotors, and so forth. Ice accumulation onaircraft engine nacelle inlets also can be problematic. Attempts havebeen made since the earliest days of flight to overcome the problem ofice accumulation. While a variety of techniques have been proposed forremoving ice from aircraft during flight, these techniques have hadvarious drawbacks that have stimulated continued research activities.One approach that has been used is so-called thermal ice protection. Inthermal ice protection, the leading edges, that is, the portions of theaircraft that meet and break the airstream impinging on the aircraft,are heated to prevent the formation of ice or to loosen accumulated ice.The loosened ice is blown from the structural members by the airstreampassing over the aircraft.

In one form of thermal ice protection, heating is accomplished byplacing an electrothermal pad(s), including heating elements, over theleading edges of the aircraft, or by incorporating the heating elementsinto the structural members of the aircraft. Electrical energy for eachheating element is derived from a generating source driven by one ormore of the aircraft engines. The electrical energy is intermittently orcontinuously supplied to provide heat sufficient to prevent theformation of ice or to loosen accumulating ice.

With some commonly employed thermal ice protection systems, the heatingelements may be configured as ribbons, i.e. interconnected conductivesegments that are mounted on a flexible backing. When applied to a wingor other airfoil surface, the segments are arranged in strips or zonesextending spanwise or chordwise along the aircraft wing or airfoil. Whenapplied to the engine inlet the heating elements can be applied eitherin the circumferential or radial orientation. One of these strips, knownas a spanwise parting strip, is disposed along a spanwise axis whichcommonly coincides with a stagnation line that develops during flight.Other strips, known as chordwise parting strips, are disposed at theends of the spanwise parting strip and are aligned along chordwise axes.Other zones, known as spanwise shedding zones, typically are positionedon either side of the spanwise parting strip at a location intermediatethe chordwise parting strips.

In one preferred form of ice protection, an electrical current istransmitted continuously through the parting strips so that the partingstrips are heated continuously to a temperature above 32 degreesFahrenheit. In the spanwise shedding zones, on the other hand, currentis transmitted intermittently so that the spanwise shedding zones areheated intermittently to a temperature above about 32 degreesFahrenheit.

One problem associated with providing such electrothermal ice protectionsystems on the nacelle inlets of aircraft engines involves providingsufficient numbers of access openings in the inner or outer barrels ofthe engine inlet for accessing and servicing the heating equipment suchas heater elements and associated components. Providing such accessopenings proximate to the leading edge of the nacelle inlet can createnon-smooth interruptions or protuberances along the otherwise smoothaerodynamic surface of the engine inlet. These interruptions orprotuberances can interfere with the desired natural laminar airflowinto and around the engine inlets, and may contribute to the creation ofunwanted noise and drag.

Therefore, there is a need for a thermal ice protection system for thenacelle inlet of an aircraft engine that provides effective iceprotection action, that includes a plurality of conveniently positionedservice access openings for use in servicing and maintaining the iceprotection system components, and that maintains a smooth aerodynamicinlet shape that results in substantially natural laminar airflow alongthe critical surfaces of the inlet.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to an aircraft enginenacelle comprising an inner support comprising an outer barrel portionand an inner barrel portion connected to the outer barrel portion; and aremovable inlet cowling attachable to the inner support, the removableinlet cowling having an outer lip, an inner lip, and a leading edgeextending between the outer and inner lips, and at least one iceprotection electrical heater associated with the leading edge of theremovable inlet cowling; wherein: the outer barrel portion has at leastone service access opening therein, and the outer lip covers the serviceaccess opening, when the inlet cowling is attached to the inner andouter barrel portions.

In another aspect, the present invention is directed to a method forservicing ice protection electrical heating equipment located between aninner barrel and an outer barrel of a nacelle. The inventive methodcomprises removing an inlet cowling having an outer lip that normallycovers at least one service access opening formed in the outer barrel tothereby uncover said at least one service access opening, said inletcowling having been previously provided with at least one ice protectionelectrical heater that is connected to said ice protection electricalheating equipment; and accessing the ice protection electrical heatingequipment through the at least one service access opening to therebyservice the same.

In yet another aspect, the present invention is directed to a nacelleinlet for an aircraft engine nacelle having an outer barrel, the nacelleinlet comprising electrical heating means for selectively heating atleast a portion of a nacelle inlet surface, and access means forselectively accessing the electrical heating means, the access meansbeing configured to promote laminar airflow over the nacelle inletsurface. The access means may comprise at least one service accessopening in the outer barrel, and a removable cowling covering theservice access opening to thereby promote laminar airflow over thenacelle inlet surface.

In still another aspect, the present invention is directed to anelectric ice protection system for an aircraft engine nacelle having aninner barrel and an outer barrel. The ice protection system comprises anengine inlet cowling having an outer lip configured for engagement withat least a portion of the outer barrel, an inner lip configured forengagement with at least a portion of the inner barrel, and a leadingedge extending between the outer and inner lips; at least one partingstrip electrical heater attached to the cowling proximate to the leadingedge; and a plurality of shed zone electrical heaters arranged side byside on either side of the parting strip electrical heater, wherein theouter barrel has at least one service access opening therein, and theouter lip is configured to cover said at least one service accessopening.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a portion of an aircraft engine having anacelle inlet thermal ice protection system according to the invention;

FIG. 2 is a perspective view of the aircraft engine of FIG. 1 with theinlet cowling detached;

FIG. 3 is an enlarged perspective view of a forward portion of theaircraft engine of FIGS. 1 and 2;

FIG. 4 is a cross-sectional view of a nacelle inlet for an aircraftengine according to the invention;

FIG. 5 is an exploded cross-sectional view of the nacelle inlet of FIG.4 with the inlet cowling detached;

FIG. 6 is a rear perspective view of a portion of an aircraft engineshowing an ice protection electrical heater arrangement on the innersurface of an inlet cowling;

FIG. 7 is a front perspective view an inlet cowling showing the iceprotection electrical heater arrangement of FIG. 6;

FIG. 8 is a rear perspective view of the inlet cowling of FIG. 7 showingplacement of ice protection electrical heaters on an inner surface ofthe inlet;

FIG. 9 a shows a cross-sectional view of a cowling in which the heateris part of an inner layer of the cowling; and

FIG. 9 b shows a cross-sectional view of a cowling in which the heateris part of an outer layer of the cowling.

DETAILED DESCRIPTION

FIG. 1 shows a portion of an aircraft engine nacelle 100 equipped withone embodiment of a nacelle inlet thermal ice protection assembly 10according to the invention. The engine nacelle 100 includes asubstantially cylindrical inner barrel 102 and a concentric outer barrel104. The nacelle inlet assembly 10 is disposed on the forward edges ofthe engine's nacelle inner and outer barrels 102, 104. The nacelle inletassembly 10 has a smooth aerodynamic shape that substantially promotesnatural laminar airflow along the forwardmost surfaces of the enginenacelle 100.

As shown in FIG. 2, the nacelle inlet assembly 10 includes a removableinlet cowling 40. The inlet cowling 40 includes an inner lip 16, anouter lip 14, and a leading edge portion 12 connecting the two. The aftedge 18 of the outer lip 14 mates with the nacelle inlet assembly 10along a split line 60. The aft edge 18 and split line 60 are positioneda substantial distance downstream of the leading edge portion 12,thereby providing a smooth, aerodynamic surface on the outer lip 14between the leading edge 12 and the split line 60. The lip cowling 40may be a single continuous 360° airfoil that covers an entire engineinlet, or may comprise a plurality of separable, arcuate cowlingsegments placed in a circumferential arrangement. In one embodiment, theseparable cowling segments have airfoil cross-sections that are placedside by side in a circumferential arrangement.

As shown in FIGS. 2 and 3, the nacelle inlet assembly 10 furtherincludes a forward support 30. The support 30 may be substantiallypermanently connected to the inner and outer barrels 102, 104 of theaircraft engine nacelle 100, or may be integrally constructed therewith.The forward support 30 provides strength and rigidity to the nacelleinlet assembly 10. As shown in FIG. 3, the forward support 30 includesan inner barrel portion 32, an outer barrel portion 36 and a forwardwall portion 34 connecting the inner and outer barrel portions. Theforward support 30 may house a plurality of spaced ice protectionelectrical heater switch boxes 28 for relaying electric power to the iceprotection system's heaters, which are described in detail below. Asshown in FIG. 6, electric power from a pylon electrical junction box 20may be supplied to one or more control boxes 26 via power feeder harness24, and may be supplied from the control box 26 to the heater switchboxes 28 via power supply harnesses 27.

As shown in FIGS. 2 and 3, the outer barrel portion 36 of the forwardsupport 30 includes a plurality of circumferentially spaced serviceaccess openings 38 therethrough. Each of the service access openings 38is located proximate to one or more associated heater switch boxes 28,and provides access to at least one of the heater switch boxes 28 fromoutside the outer barrel portion 36.

As shown in FIGS. 1 and 4, when the inlet cowling 40 is installed on theforward support 30, the outer lip 14 covers each of the respectiveservice access openings 38 in the outer barrel portion 36 of the forwardsupport 30. Therefore, this arrangement precludes the need for anindividual cover for each service access opening 38. This arrangementalso provides a continuous smooth aerodynamic lip surface 14 proximateto the leading edge 12 that helps promote natural laminar airflow acrossthe nacelle during flight.

As shown in FIGS. 1, 2 and 3, the inlet cowling 40 is connected to theforward support 30 along both aft edges 18, 19 by pluralities ofsuitable removable fasteners 50. For example, the fasteners 50 mayinclude bolts, rivets, or other suitable fasteners having substantiallyflush profiles. Preferably, the fasteners are of a type that is easilyinstalled and removed by service personnel.

Further details of the nacelle inlet assembly 10 are shown in FIGS. 4and 5. As shown in FIG. 4, the inlet cowling 40 substantially conformsto the shape of the forward support 30 except for a ice protectionelectrical heater pocket 80 formed between the leading edge 12 of thecowling 40 and the forward wall 34 of the forward support 30. The pocket80 provides space for a plurality of ice protection ribbon heaters 70 a,70 b, 70 c, 72 mounted on the inner surface of the leading edge 12 ofthe inlet cowling 40, as well as for an electrical connector 76 whichconnects to electrical connector 74 mounted on the forward wall 34.

The first and second electrical connectors 74, 76 automatically connectto one another, making a plug and socket-type connection, when the inletcowling 40 is adjusted from a first position in which it is separatedfrom the inner and outer barrel portions to a second position in whichit covers the inner and outer barrel portions. Alternatively, connectors74 and 76 may be electrically connected (or disconnected) by manuallyattaching (or detaching) a cable extending between the two. Electricpower is supplied to the heaters 70 a, 70 b, 70 c, 72 from the heaterswitch boxes 28 via heater supply harness 29 and electrical connectors74. In the embodiment shown, the electrical connectors 74 are mounted onthe forward wall 34 of the forward support 30.

As shown in FIG. 4, the inner barrel portion 32 of the forward support30 may include an acoustic portion 33, known to those skilled in theact, for attenuating engine noise. In the arrangement shown, the aftedge 19 of the inner lip 16 adjoins the forward support 30 at a positionthat is immediately forward (or upstream of) of the acoustic portion 33.

FIGS. 4 and 5 show the maintenance and service access features of thenacelle inlet assembly 10. With the inlet cowling 40 removed, theservice access openings 38 are uncovered, and various ice protectionelectrical heating equipment such as the heater switch boxes 28, heatersupply harnesses 29, power supply harnesses 27, and electricalconnectors 74 can be easily accessed by service personnel extending hisor her hand 150 through the service access openings 38. In addition, theremoved inlet cowling 40 provides ready access to the ice protectionelectrical heaters 70 a, 70 b, 70 c, 72, and associated electricalconnectors 76 mounted on the inside surfaces of the cowling 40. Ifrequired, the removable inlet cowling 40 can be easily replaced with asecond inlet cowling 40, and can be separated from an associated enginenacelle 100 for remote service or repair.

FIGS. 6 and 7 show one possible arrangement for the ice protectionelectrical heaters 70 a, 70 b, 70 c, and 72. First, one or more partingstrip heaters 72 are provided along an inner surface of the leading edge12 of the removable cowling 40. Preferably, each parting strip heater 72is positioned to be substantially coincident with an airflow stagnationline along the engine inlet's leading edge 12. Second, a plurality ofshed zone heaters 70 a, 70 b, 70 c are provided in substantially side byside relation along the inside surface of the leading edge 12, therebysubstantially covering the entire inside surface of the leading edge 12.Although adjacent shed zone heaters may abut one another if they areelectrically isolated from each other, more preferably, they are spacedapart from one another by a gap of between about 0.04″ to about 0.5″;other gap spacings may also be employed. In this arrangement, power canbe supplied substantially constantly to the parting strip heater(s) 72to provide more or less continuous ice protection along the airflowstagnation line.

Power also can be intermittently supplied to the shed zone heaters 70 a,70 b, and 70 c to shed accumulated ice on either side of the stagnationline. In the arrangement shown, for example, pulses of electrical powermay be supplied in sequence to shed zone heaters 70 a, to shed zoneheaters 70 b, to shed zone heaters 70 c, again to shed zone heaters 70a, etc. The distribution of electric power to the various heaters 70 a,70 b, 70 c, and 72 is controlled by one or more electrical supplycontrol boxes 26. This cyclic rationing of electric power between thevarious shed zone heaters 70 a, 70 b, 70 c acts to minimize the amountof electric power that must be derived from an aircraft's finiteelectrical generation capacity, while effectively providing iceprotection to the engine inlet's leading edge 12.

It is understood that one may operate the heating system such that allshed zone heaters designated 70 a are active for a first period of time,then all shed zone heaters designated 70 b are active for a secondperiod of time and finally all shed zone heater designated 70 c areactive during a third period of time. It is further understood thatthese three periods of time need not necessarily be of equal durationand that they need not necessarily be contiguous—i.e., there may be someintervening periods during which none of these three sets of shed zoneheaters is on. It is also understood that other numbers of sets ofheaters may be provided—for instance, two sets, four sets, or five sets,etc.

FIG. 8 shows one possible arrangement for installing the heaters 70 a,70 b, 70 c, 72 on the inner surface of the inlet cowling 40. In thisarrangement, a parting strip heater 72 is mounted on the inner surfaceof the lip cowling 40 proximate to the underside of the airflowstagnation line at the leading edge 12. Next, a plurality of shed zoneheating pads 70 a, 70 b, 70 c are applied over the parting strip heater72 such that the heater pads 70 a, 70 b, 70 c cover substantial portionsof the inside surface of the leading edge 12 on each side of the partingstrip heater 72. The heaters 70 a, 70 b, 70 c, 72 may be any type ofsubstantially flat, foil, or ribbon heater capable of supplyingsufficient heat energy to the cowling 40 to effectively de-ice thecowling 40 while in service. The heating elements 70 a, 70 b, 70 c, 72may be configured as “ribbons”, i.e. interconnected conductive sections,that are mounted on a flexible backing. For example, the low-powerelectric heaters 70 a, 70 b, 70 c, 72 may be like the ice protectionelectrical heaters described in U.S. Pat. No. 5,475,204, assigned toGoodrich Corporation. Alternatively, the ice protection electricalheaters 70 a, 70 b, 70 c, 72 may be like those described in U.S. patentapplication Ser. No. 10/840,736, filed on May 6, 2004. The disclosuresof U.S. Pat. No. 5,475,204 and U.S. patent application Ser. No.10/840,736 are hereby incorporated by reference in their entireties. Andso, when in use, adjacent portions of the inlet cowling may besequentially heated by alternatingly supplying current to the pluralityof electrical ribbon heaters. Suitable electric wiring 74 supplieselectric power to the ice protection electrical heaters 70 a, 70 b, 70c, 72 from one or more heater switch boxes 28.

FIG. 9 a shows a cross-section of an inlet cowling 40 a in which the iceprotection electrical heater is spaced apart from the ice 950 by one ormore layers. The structural skin 904 of the cowling 40 a providessupport for the layers above. These layers include a first insulationlayer 906, a heater layer 908 atop the first insulation layer, a secondinsulation layer 910 atop the heater layer 908, and an erosion shield912 atop the second insulation layer 910. Heat from the heater layer 908passes through the second insulation layer 910 and the erosion shield tomelt the ice 950.

In one embodiment, the thickness of the inlet cowling is on the order of0.1″-0.2″. The structural skin 904 is formed of a metallic or compositematerial having a thickness between about 0.02″ and 0.10″; the firstinsulation layer 906 is formed of an electrically inert (i.e.,electrically insulative) material having a thickness between about 0.01″and 0.04″; the heater layer 908 comprises electrical heaters formed of ametallic or conductive material on a nonconductive plastic film or othersubstrate and having a thickness between about 0.005″ and 0.020″; thesecond insulation layer 910 is formed of an electrically inert (i.e.,electrically insulative) but thermally conductive material having athickness between about 0.01″ and 0.04″; and the erosion shield 912comprises a thermally conductive metallic skin or coating having athickness between about 0.002″ and 0.020″.

Instead of being mounted on the inner surface of the inlet cowling 40 asshown in FIGS. 4-6, the ice protection electrical heaters 908 may bemounted on the outer surface. When positioned on the outer surface, theice protection electrical heaters are more directly exposed to the iceand so the energy efficiency of the system may improve. Through holesmay be formed in some of the underlying layers of the cowling 40 atspaced apart intervals to accommodate wires and other connections todeliver current to the ice protection electrical heaters. FIG. 9 b showsa cross-section of an inlet cowling 40 b in which the heater forms theouter surface of the cowling 40 b. Again, the structural skin 924 of thecowling 40 b provides support for the layers above. These layers includea first insulation layer 926, and a heater layer 928 atop the firstinsulation layer 924, all having substantially the same composition andthickness ranges discussed above with respect to FIG. 9 a. In thisinstance, however, the heater layer 928 is exposed to the elements andso must also serve as the erosion shield.

In both FIGS. 9 a and 9 b, a wire or cable 930 provides current to theheater layers 908, 928. preferably, the wire is connected to the heatervia an electrical solder connection 932, as seen in these figures. It isunderstood in these figures that each of the heater layers may comprisemultiple individual ice protection electrical heaters.

Engine inlets in accordance with the present invention may realizeefficient ice protection with lower weight inlet structure, as comparedto a conventional hot air thermal anti-ice (TAI) system. Furthermore,eliminating the pressures and temperatures associated with a traditionalTAI system simplifies certain aspects of nacelle design. For instance,traditional split lines between the inlet major components are driven bythe thermal anti-ice system and the acoustic requirements. Theelectrical system of the present invention generally does not rely uponthese limitations and may therefore allow for these locations to beoptimized for other design criteria. As an example, moving thetraditional split line between the inlet lip and the outer barrel aftimproves the aerodynamic performance of the inlet and allows the lip tobe incorporated into a design that promotes natural laminar flow whilealso covering an access opening.

The above description of various embodiments of the invention isintended to describe and illustrate various aspects of the invention,and is not intended to limit the invention thereto. Persons of ordinaryskill in the art will understand that certain modifications may be madeto the described embodiments without departing from the invention. Allsuch modifications are intended to be within the scope of the appendedclaims.

1. An aircraft engine nacelle comprising: an inner support comprising anouter barrel portion and an inner barrel portion connected to the outerbarrel portion; and a removable inlet cowling attachable to the innersupport, the removable inlet cowling having an outer lip, an inner lip,and a leading edge extending between the outer and inner lips, and atleast one ice protection electrical heater associated with the leadingedge of the removable inlet cowling; wherein: the outer barrel portionhas at least one service access opening therein, and the outer lipcovers the service access opening, when the inlet cowling is attached tothe inner and outer barrel portions.
 2. The aircraft engine nacelleaccording to claim 1, further comprising: ice protection electricalheating equipment that is: located between the inner barrel portion andthe outer barrel portion, and accessible through said access opening,when the inlet cowling is detached from the inner and outer barrelportions.
 3. The aircraft engine nacelle according to claim 2, whereinthe electrical heating equipment comprises at least one heater switchbox.
 4. The aircraft engine nacelle according to claim 1, wherein theice protection electrical heater comprises at least one parting stripheater positioned along a leading edge of the removable inlet cowling.5. The aircraft engine nacelle according to claim 4, wherein the iceprotection electrical heater further comprises a plurality of shed zoneelectrical heaters arranged side by side on either side of the partingstrip electrical heater.
 6. The aircraft engine nacelle according toclaim 5, wherein the at least one parting strip electrical heater, andthe plurality of shed zone electrical heaters, are arranged on an innersurface of the inlet cowling.
 7. The aircraft engine nacelle accordingto claim 5, wherein the at least one parting strip electrical heater,and the plurality of shed zone electrical heaters, are arranged on anouter surface of the inlet cowling.
 8. The aircraft engine nacelleaccording to claim 5, further comprising: at least one heater controllerconfigured to selectively supply pulses of electrical power to the shedzone electrical heaters.
 9. The aircraft engine nacelle according toclaim 1, wherein an axial length of the outer lip is greater than anaxial length of the inner lip.
 10. The aircraft engine nacelle accordingto claim 1, wherein the inlet cowling has an aerodynamic profile thatpromotes laminar airflow across the outer lip.
 11. The aircraft enginenacelle according to claim 1, wherein the inlet cowling comprises aplurality of arcuate inlet cowling segments.
 12. The aircraft enginenacelle according to claim 11, wherein at least one of said plurality ofinlet cowling segments comprises said outer lip that covers the at leastone service access opening, when the inlet cowling is attached to theinner and outer barrel portions.
 13. The aircraft engine nacelleaccording to claim 11, wherein the ice protection electrical heatercomprises at least one parting strip heater positioned along a leadingedge of at least one of said plurality of inlet cowling segments.
 14. Amethod of servicing ice protection electrical heating equipment locatedbetween an inner barrel and an outer barrel of a nacelle, comprising:removing an inlet cowling having an outer lip that normally covers atleast one service access opening formed in the outer barrel to therebyuncover said at least one service access opening, said inlet cowlinghaving been previously provided with at least one ice protectionelectrical heater that is connected to said ice protection electricalheating equipment; and accessing the ice protection electrical heatingequipment through the at least one service access opening to therebyservice the same.
 15. The method of claim 14, further comprising:breaking at least one electrical connection between the at least one iceprotection electrical heater and the ice protection electrical heatingequipment, prior to servicing the ice protection electrical equipment.16. The method of claim 15, wherein the at least one electricalconnection is automatically broken during the removing step.
 17. Themethod of claim 14, wherein the accessing step comprises inserting ahand through the service access opening.
 18. A nacelle inlet for anaircraft engine nacelle having an outer barrel, the inlet comprising:electrical heating means for selectively heating at least a portion of anacelle inlet surface; access means for selectively accessing theelectrical heating means, the access means being configured to promotelaminar airflow over the nacelle inlet surface.
 19. The nacelle inletaccording to claim 18, wherein the electrical heating means comprises atleast one heater switch box.
 20. The nacelle inlet according to claim18, wherein the electrical heating means comprises at least one flexibleribbon heater.
 21. The nacelle inlet according to claim 18, wherein theaccess means comprises at least one service access opening in the outerbarrel, and a removable cowling covering the service access opening tothereby promote laminar airflow over the nacelle inlet surface.
 22. Anelectric ice protection system for an aircraft engine nacelle having aninner barrel and an outer barrel, the ice protection system comprising:an engine inlet cowling having an outer lip configured for engagementwith at least a portion of the outer barrel, an inner lip configured forengagement with at least a portion of the inner barrel, and a leadingedge extending between the outer and inner lips; at least one partingstrip electrical heater attached to the cowling proximate to the leadingedge; and a plurality of shed zone electrical heaters arranged side byside on either side of the parting strip electrical heater, wherein: theouter barrel has at least one service access opening therein, and theouter lip is configured to cover said at least one service accessopening.